Thermionic converter



L.. W. CHUBB THERMIONIC CONVERTER.

Filed May 1`5. 1917 INVENTOR Lew/5 W bl/bb.

AoRNEY Load Patented May 25, 1926.

UNITED vSTATES 1,585,766 PATENT OFFICE.

LEWIS W. CHUBB, OF EDGEWOOD PARK, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC 8c MANUFACTURING COMPANY,A CORPORATION 0F PENNSYL- VANIA.

THERMIONIC CONVERTER.

My invention relates to electric apparatus of the type wherein an electron blast is produced within a closed container as, for example, in converters and in vacuum lamps, and it has for its object to provide appara'- tus of the character designa-ted which shall be simple and inexpensive in manufacture and highly effective in operation.

More specifically, the object of -my invention is to provide a vacuum-type converter of the hot cathode type which in normal operation shall re uire no auxiliary heating current, the re ative size, location and specific electron emissivities of the different electrodes being such that half cycles of current of one polarity are permitted to pass freely between a given pair ofelectrodes but, with half cycles of the other polarity, only sufficient current is permitted to pass to maintain the nominal cathode at an elec tron-emitting temperature.`

It is known that a refractor filament comosed, for example, of tungsten, may have lts specific electron emissivity, at a given temperature, greatly increased by the admiX- ture of a small percentage of foreign substance such, for example, as thorium or thorium oxide. I am not prepared to state Whether the 'additional electrons are derived from the foreign substance or whether there is an action similar to catalysis whereby the v foreign substance causes a much more profuse emission from the tungsten itself. Furthermore, I am not in a position to state whether the foreign substance as, for example, thoria is active in its combined state or whether it is reduced to the metallic state before performing its electron-modifying function. In the practice of my invention, however, itis unnecessary to lbe restricted to any specific theory ofop'eration and the above suggestions are merely offered as an aid to the public in understanding my invention.

While material containing thorium gives extremely good results and may well be employed in the practice of my invention, I find that good results may be obtained by employing zirconium or its compounds as, for example, zirconia..

Fig. 1 of the accompanying drawing is a diagrammatic view, partially in section and partially in elevation, of a vacuum-type converter embodying a preferred form of my invention; vand Fig. 2 'is a similar view of a modification of the structure shown in Fig. 1.

Vacuum-type converters are well known 1n which the cathode is formed into a refractory filament which is maintained at incandescence b any suitable means such, forV eX- ample, as y, the passage of auxiliary heating current therethrough. Said incandescent cathodes have in the past been formed, either of refractory elements such, for example, as

carbon, platinum, tungsten or molybdenum,

or,`in certain cases, they have been formed of refractory filaments covered by oxide coatings because of the high electron emissivity of certain refractory oxides.

In the practice of my invention, I prefer to form the cathode from tungsten or molybdenum containing a small admixture ofv foreign matter, as before mentioned, and by this means I am enabled to obtain an enormous electron discharge with the expenditure of but little energy in heating the electrode. Thus, I am enabled to provide either a very small heating source for the cathode, for a given capacity of converter, or I am enabled to provide a converter of very small dimensions having a very high capacity.

Furthermore, by employing a vacuumtype converter embodying two electrodes having dissimilar electron emissivities at a given temperature, I am enabled to obtain a pronounced rectifyingaction while maintaining the entire converter apparatus at an extremely high temperature. Thus, the two electrodes may be mounted in close proximity so that each tends to heat the other and no special precautions need be taken to ensure the cooling of the anode as is the case with the ordinary vacuum-type converter. Furthermore, I am enabled to still further conserve the heat in apparatus of the character designated by providing a suitable heat insulating jacket or equivalent means.

' I preferably so -arrange the size, mounting able number of electrons which bombard the nominal cathode but also permitting the flow of a small amount of reverse current. The joint action of said reverse current How and o-f said bombardment is to maintain the nominal cathode at an electron-emitting temperature during said second-mentioned half cycles, thus permitting the entire device to operate continuously with no source of auX- iliary heating current for either of the filaments. While l recognize that the flow of reverse current is, in general undesirable, nevertheless, with many types'of load, such, for example, as in battery charging, the effeet of the small amount of reverse current dow which is necessary may be disregarded.

Referring to the drawing for a more detailed understanding of my invention, I s how a vacuum-type `converter at 1 comprising a highly evacuated container 2 supplied with an anode 3 and with a cathode 4. The anode 3 may either be a mass of refractory material such, for example, as carbon or tungsten or it may take the form of a filament of tungsten, as shown. The cathode 4 is in the.

form of a closely wound filament of tungsten-thorium or tungsten-zirconium mixture or a tungsten filament coated with thorium or zirconium in any desired manner. The anode 3 may 'be heated by a suitable auxiliary source 5 and, in like manner, the anode 4 may be heated by a suitable auxiliary source 6. An alternating electromotive force is impressed between the electrodes 3 and 4 by any suitable means such, for example, as the secondary winding 'I of a transformer 8 havin a primary winding 9 energized from suitab e alternating-current mains. A load demanding unidirectional current is shown at 10.

Having thus. described the arrangement of a system embodying my invention, the operation is as follows. Upon energizing the transformer 8 and closing the circuits from the auxiliary current sources 5 and 6, an alternating electroinotive force, is impressedl lbetween the two electrodes and said electrodes are raised to incandescence. vastly more profuse emission of electrons from the cath-ode than from the anode3 permits the free passage of current from the anode 3 to the cathode 4 but the lack of current carriers greatly hinders the How of current in the opposite direction.

Having initiated operation in this manner, .the flow of auxiliary heating current may 'be prevented and the device will continue to operate, obtaining its entire heating action 'from the alternating-current supply as has been hereinbefore fully described.

`While l have shown the anode 3 in the form ofv a heated filament, it is obvious that the device will be operable were no heat supplied to said lament or if the anode were The aucunes given the form of a cup or 'sphere as is usual. i.

Referring to'the form of .my invention shown in Fig. 2, a container 2 is provided with an anode 3, in the form of a centrally disposed coil, and with a cathode 4 in the form of a straight filament axiall disposed within the coiled anode 3. The e ectrodes 3 and`4 are formed respectively of tungsten and of tungsten alloy as in the structureof Fig/1. Said electrodes'may be initially heated from suit-able current sources 5 and 6through switches 11 and 12. Energy for the operation of the converter is derived from a transformer 8. The container 2 may be surrounded with any suitable heat-insulating means, such, for example, as a fibrous layer 13. In operation, the 'switches 11 and 12 are iirst'closed, raising the respective electrodes tol incandescence and load current then flows from the secondary winding 7. A small portion of each of alternate vcurrent waves flows from the electrode 4 as an anode to the electrode 3 as a cathode and substantially all portions of therremaining'current waves flow from the electrode 3 as an anode to the electrode 4 as a cathode. Each electrede, when operating as a cathode, bombards the other one. `When the electrode 3 is a cathode and the electrode 4 is an anode, there are but relatively few electrons emitted but the electrode 4, by reason of its centrally focal position, is suiliciently heated thereby to maintain its incandescence. When the electrode 4 is a cathode and the electrode 3 is an anode, the profuse electron emission of the electrode 4 is ample to adequately heat the surrounding electrode 3. The heat insulatin layer 13 conserves a large portion of the eat generated in the converter and aids in maintaining the respective electrodes at a high temperature. Thus, after the device has been brought into operation, the

switches 11 and 12 may be opened and the respective electrodes thereafter maintain a suitable operating temperature solely by virtue of the heat produced by the iiow of load current.

Not only is my invention applicable to converters of the character designated but it may also be used with any form of apparatus embodying pure electron emission such, for example, as certain Aforms of X- ray tubes and of lamps wherein the light source is a refractory body maintained at incandescence lby electron bombardment such, for example, as shown in my copending application, Serial No. 129,980, filed Nov. 7. 1916. and assigned to the Westing-- I and I desire, therefore, that Aonly such limi- 'having a relatively high electron emissivity when heated to incandescence, means for maintaining both of said electrodes at incandescence, and means for applying an ,alternating electromotive force between said electrodes.

2. In vacuum-type electric apparatus, the combination with an electrode composed of a refractory metal having a relatively low electron emissivity when heated to incandescence, of an electrode composed of a metallic mixture having a relatively high electron emissivity when heated to incandescence, means for maintaining both of said electrodes at incandescence, and means for applying an alternating electromotive force between said electrodes.

3. In vacuum-type electric apparatus, the combination with a ilamentary electrode composed of a refractory metal having a relatively low electronemissivity when heated to incandescence,'of an electrode composed of a zirconium bearing body having a relatively high electron emissivity 'when heated to incandescence, means for maintaining both of said electrodes at incandescence, and means for applying an alternating electromotive force between said electrodes. v

i. In vacuum-type electric apparatus, the combination with a yilamentary electrode composed of a refractory metal having a relatively low electron emissivity when heated .to incandescence, 'of an electrode composed of a tungsten-zirconium mixture, means for maintaining both of said electrodes at incandescence, and means for applying an alternating electromotive force between said electrodes.

5. A vacuum-type converter embodying two electrodes having a diierent electron emissivity when lequally heated and means for heating both of said electrodes.

6. The method of operating a vacuumtype converter from .a source of alternating current, said converter embodying two electrodes, which comprises permitting free passage to are current therethrough during half cycles -of said source of alternating current 'of one polarity and permitting passage of only suilicient arc current during half cycles A of said source of alternating current of the other polarity to maintain said device in an operative condition.

7. The method of operating a vacuumtype converter from a source of alternating current, said converter embodying two electrodes, which comprises generatin sufficient electrons therein during half-cyr: es of one polarity to ermlt the free flow of arc current theret rough, and generating only suiicient electrons therein during. half cycles of the other polarity to permit the' n fiow o f that amount of arc current necessary to maintain the nominal cathode at anelec- 'tron-emitting temperature.

8. In vacuum-type electric apparatus, the

combination with a nominal cathode, of af nominal anode, connections from said electrodes to the respective terminals of a source of alternating current, and means permitting the flow of only' suicient are current through the apparatus when said nominal cathodeis positlve to maintain said electrode at an electron-emitting temperature, said device permitting the free passage of arc current when said nominal cathode is negative in polarity.

9. In vacuum-type electric apparatus, the combination with a nominal cathode composed of material of relatively high specific lelectron emissivity, of a nominal anode of relatively low specific electron emissivity, and connections from said electrodes to the respective terminals of a source of alternating current, the electron emission of the said nominal cathode when negative beingv suficient to permit the passage of substantially the entire current wave and the electron emission of said nominal anode, when negative, being only suiicient to maintain said nominal cathode at an electron-emitting temperature by the joint effect of electron bombardment and of reverse load current.

10. `In vacuum-type electric apparatus, the combination with a closed'container, of two electrodes therein composed of substances of differing specific electron emissivities at a given temperature and connections fromsaid electrodes to the respective terminals of a source of alternating current, the relative size and emissivities of the two electrodes being such that during half cycles when the electrode. of high emissivity is negative, substantially'all the current is permitted to pass, bombarding the electrode of low emissivity only enough to maintain said electrode at an electron-emitting temperature, and during the alternate half cycles,

only suicient electrons are emitted by the elect-rode' of low emissivity to cause such current flow and electron bombardment as to maintain thev electrode of high emissivity at an electron-emitting temperature.

11. In a vacuum-type electric apparatus, the combination with an electrode having relatively low electron' emissivity, o a filamentary electrode having a relatively high electron emissivity, means for maintaining -t both-of said electrodes in electron-emitting condition, and means for applying an a1- ternating electromotive force' between said electrodes.

12. A vacuum-type converter embodying two electrodes having different electronemission characteristics and means for maintaining each of said electrodes in an electron emitting condition.

13. A vacuum-type converter embodying two electrodes having diierent electronemissivity characteristics and permitting alternating current to pass therebetween in both directions, but to a different degree obtained.

. two electrodes of different electron-emitting roperties and means for impressing an aternating potential therebetween tol cause a large current fiow in one direction and a small current ow in the other direction, whereby a net unidirectional current is In testimony whereof, I have hereunto subscribed my name this 27th day of April lLEWIS IV. CHUBB. 

